Some companies like Merc have this magical overtrade (OT) thing, which means the sticker price is much higher than what you can expect to pay
The OT has Nothing to do with the scrap car value.
Say a car SRP = 180k
OT is what the agent gives as a discount. The condition is you must trade in a car. Any car ( only condition is that you own it > 6months apparently)
Say OT = 10k
Then whatever value you get for your car is dependant on the SALE price of your current car. Eg if you have a 5 year old Camry and you get an offer of 50k for it.
So you pay 180-10 net, then minus the 50k for the Camry.
The net price is 170k, PLUS whatever freebies they give. That's the ad trick. They will add in the freebies which you get if you get a loan.
Eg Nano, DVR, service credits, solar film etc, things which I have posted earlier. Say all these have a net value of 10k, then they will say your car is 180-OT-Freebies or 160k.
So the ad will say, get a C180 for 160k.